(P137) Seeing Is Believing: Concerns and Solutions in Implementing Magnetic Resonance Image–Guided Radiation Therapy

OncologyOncology Vol 29 No 4_Suppl_1
Volume 29
Issue 4_Suppl_1

The system has been used since January 2014 to treat patients. Based on the results of ongoing machine and patient-specific tests and with independent confirmation, the treatments are being delivered accurately and safely.

Olga L. Green, PhD, H.O. Wooten, PhD, Yanle Hu, PhD, Rojano Kashani, PhD, Lakshmi Santanam, PhD, Harold Li, PhD, Sasa Mutic, PhD; Washington University School of Medicine

PURPOSE: We describe the potential problems and solutions developed in initiating first treatments with a commercially available magnetic resonance image–guided radiation therapy (MR-IGRT) system. Specifically, we address the following: (1) effect of magnetic fields on dose distributions, (2) patient and staff safety in the presence of magnetic and radiation fields, and (3) quality assurance for MR-IGRT.

MATERIALS AND METHODS: The foremost problem of integrating an MRI system with a radiation delivery system has been solved by combining a 0.35-T split-doughnut MRI with a gantry carrying three 60 Co sources. This system was installed in our institution in 2012, and since then, we have conducted ongoing work toward its clinical implementation. The problem of the effect of magnetic fields on dosimetric distributions was investigated by comparing measurements with an in-house phantom to Monte Carlo calculations. The problem of patient and staff safety was addressed by measuring the specific absorption ratio (SAR) to ensure that it was safe for patients to be imaged continuously while being treated and by implementing safety checks in our daily workflow. The problem of quality assurance for MR-IGRT was solved by establishing the accuracy of measurement devices (ionization chambers, detector arrays) in the presence of the magnetic field and developing tests that checked both the geometric and dosimetric accuracy of the system on a daily, weekly, monthly, and annual basis. Independent confirmation of dosimetric accuracy was provided by the Imaging and Radiation Oncology Core (IROC) service-reference dosimetry via optically stimulated dosimeters and overall delivery quality via the head-and-neck phantom (film and thermoluminescent dosimeters).

RESULTS: The 0.35-T magnetic field was found to have a negligible effect on dose distributions for the type of patient plans used clinically. The measured SAR value was 1.14 W/kg, which ensured that patients do not experience excessive heating during the ongoing real-time imaging at four frames per second. MR training was conducted for all staff, and procedures were implemented to ensure that patients were cleared to be MR-safe before every treatment. Quality assurance included spatial integrity and homogeneity of the MR field, MR and RT isocenter coincidence, and pre- and posttreatment patient-specific QA. Satisfactory results were reported by the IROC for four independent OSL (Optically Stimulated Luminescence) reference dosimetry checks and the head-and-neck phantom.

CONCLUSION: The system has been used since January 2014 to treat patients. Based on the results of ongoing machine and patient-specific tests and with independent confirmation, the treatments are being delivered accurately and safely.

Proceedings of the 97th Annual Meeting of the American Radium Society - americanradiumsociety.org

Articles in this issue

(P005) Ultrasensitive PSA Identifies Patients With Organ-Confined Prostate Cancer Requiring Postop Radiotherapy
(P001) Disparities in the Local Management of Breast Cancer in the United States According to Health Insurance Status
(P002) Predictors of CNS Disease in Metastatic Melanoma: Desmoplastic Subtype Associated With Higher Risk
(P003) Identification of Somatic Mutations Using Fine Needle Aspiration: Correlation With Clinical Outcomes in Patients With Locally Advanced Pancreatic Cancer
(P004) A Retrospective Study to Assess Disparities in the Utilization of Intensity-Modulated Radiotherapy (IMRT) and Proton Therapy (PT) in the Treatment of Prostate Cancer (PCa)
(S001) Tumor Control and Toxicity Outcomes for Head and Neck Cancer Patients Re-Treated With Intensity-Modulated Radiation Therapy (IMRT)-A Fifteen-Year Experience
(S003) Weekly IGRT Volumetric Response Analysis as a Predictive Tool for Locoregional Control in Head and Neck Cancer Radiotherapy 
(S004) Combination of Radiotherapy and Cetuximab for Aggressive, High-Risk Cutaneous Squamous Cell Cancer of the Head and Neck: A Propensity Score Analysis
(S005) Radiotherapy for Carcinoma of the Hypopharynx Over Five Decades: Experience at a Single Institution
(S002) Prognostic Value of Intraradiation Treatment FDG-PET Parameters in Locally Advanced Oropharyngeal Cancer
(P006) The Role of Sequential Imaging in Cervical Cancer Management
(P008) Pretreatment FDG Uptake of Nontarget Lung Tissue Correlates With Symptomatic Pneumonitis Following Stereotactic Ablative Radiotherapy (SABR)
(P009) Monte Carlo Dosimetry Evaluation of Lung Stereotactic Body Radiosurgery
(P010) Stereotactic Body Radiotherapy for Treatment of Adrenal Gland Metastasis: Toxicity, Outcomes, and Patterns of Failure
(P011) Stereotactic Radiosurgery and BRAF Inhibitor Therapy for Melanoma Brain Metastases Is Associated With Increased Risk for Radiation Necrosis
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